Inside Freesat

Originally published in Personal Computer World as a part of the article All about Freesat

Inside Freesat

Freesat’s technical specification is largely based around the Electronic Programme Guide (EPG). In order to co-exist with Sky’s systems there has to be some co-operation with Sky, who lease some of the transponders, and some changes to the way data is sent to receivers.

The DVB standard includes ‘Service Information,’ or SI, which carries EPG data. But because Sky has their own SI already being carried on the transponders used, Freesat has to slot their own data alongside. Each element of the data stream in digital broadcasting has a packet ID (PID), and to co-exist with Sky, Freesat’s data has to use non-standard PIDs – which is one reason why existing free to air receivers won’t see it. Another is that the text is compressed (fully deciphering that compression is at the core of the work needed for MythTV to see the EPG).

As well as basic EPG data, Freesat is broadcasting metadata that indicates which programmes are part of a series, which will enable recorders to automatically record the whole set, as well as track changes to schedules and resolve clashes.

In addition to the EPG data on the channel transponders, there’s a full EPG broadcast from the Eurobird 1 satellite – at 28.5° East, it’s close enough to Astra 2 that dishes will pick up both.

Interactivity is based on an enhanced version of MHEG5 1.06, the system used on Freeview; the additions allow for the mandatory Ethernet port to be used as a return channel by interactive applications, and for receiving IPTV streams.

HD-capable boxes have to support the H.264 codec and DVB-S2, but it’s not mandatory on SD ones; the word from Freesat is that all boxes must have Ethernet, and IPTV services will be available on all receivers “where technically possible.” At PCW, we’d recommend an HD box just to be sure, so you’ll be able to receive H.264 content via the internet too.

Besides the technical requirements, Freesat also mandates some interface issues – like the minimum number of channels shown on the EPG, and the fact that the Genre selection screen is always shown when you enter the guide, making it two presses to get to the listings – which is one of the most annoying and, frankly, bonkers user interface decisions we’ve seen in a while. Within those specs, however, there’s scope for manufacturers to change things around, so on-screen displays and the keys used for some functions will be different. That means that while Freesat boxes won’t have the uniformity of Sky receivers, nor will they have the huge differences found amongst Freeview boxes.

Published by Nigel

Freelance journalist since 1995, before that editor of Computer Buyer. I've written for many titles, including Personal Computer World, Computer Active, and Register Hardware. I also run the successful Toppy.org.uk site for users of Topfield PVRs.
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